Feeding Buzzzzzzzz!

Friday, April 28, 2017

by Lincoln Park Zoo

in

Nature Boardwalk

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As part of our ongoing research monitoring bats around the Chicago region, we’ve set out acoustic (sound) detectors at several sites to see how bats are using the city. Although bats can see, they primarily use sound to navigate their environment and look for food. Acoustic detectors are a great way to study bats because they record the ultrasonic echolocation calls that we can’t hear. Using software and some expertise, these calls (usually) can tell us which species are present.

Spring has sprung, and we are seeing the emergence of plants, insects, and the return of migrating birds and bats to the Chicago region! Although our detector has been out since January, we saw a big increase in bat activity recorded at Nature Boardwalk last week. Upon reviewing the calls, we were excited to see four of the eight species we might expect to see in this region: big brown bats, silver-haired bats, hoary bats, and Eastern red bats. But we were even more excited to see several feeding buzzes among the calls!

Above: This is a spectrogram (graphical representation of sound) of a big brown bat (Eptesicus fuscus) call. The frequency (kHz) is on the y-axis, and the time (msec) is on the x-axis. Note that the pulses of the call get higher in frequency, and then closer and closer together (faster and faster), indicating a feeding buzz!

Feeding buzzes occur when a bat discovers a prey item (such as a mosquito) and emits rapid echolocation pulses to hone in on its prey. Feeding buzzes are difficult to record because the sound dissipates faster in the environment than a typical navigational call, so we don’t record them often. But when we do, it’s a good indication that a site is providing valuable foraging habitat for bats.

We renovated Nature Boardwalk in 2010 from a traditional recreational pond to a natural wetland ecosystem to provide a respite for wildlife (and humans) from the bustling city. Over the years we have observed more than 180 bird species and several species of mammals, turtles, dragonflies, and pollinators using the space. Bats are under many threats right now, including habitat loss. It’s thrilling to see that Nature Boardwalk is doing its part to provide important habitat for these vulnerable species.

Above: an acoustic detector used to record bat calls at Nature Boardwalk.